On Mon, Mar 03, 2008 at 02:10:17PM +0100, Nick Piggin wrote: > On Mon, Mar 03, 2008 at 01:51:53PM +0100, Andrea Arcangeli wrote: > > On Mon, Mar 03, 2008 at 04:29:34AM +0100, Nick Piggin wrote: > > > to something I prefer. Others may not, but I'll post them for debate > > > anyway. > > > > Sure, thanks! > > > > > > I didn't drop invalidate_page, because invalidate_range_begin/end > > > > would be slower for usages like KVM/GRU (we don't need a begin/end > > > > there because where invalidate_page is called, the VM holds a > > > > reference on the page). do_wp_page should also use invalidate_page > > > > since it can free the page after dropping the PT lock without losing > > > > any performance (that's not true for the places where invalidate_range > > > > is called). > > > > > > I'm still not completely happy with this. I had a very quick look > > > at the GRU driver, but I don't see why it can't be implemented > > > more like the regular TLB model, and have TLB insertions depend on > > > the linux pte, and do invalidates _after_ restricting permissions > > > to the pte. > > > > > > Ie. I'd still like to get rid of invalidate_range_begin, and get > > > rid of invalidate calls from places where permissions are relaxed. > > > > _begin exists because by the time _end is called, the VM already > > dropped the reference on the page. This way we can do a single > > invalidate no matter how large the range is. I don't see ways to > > remove _begin while still invoking _end a single time for the whole > > range. > > Is this just a GRU problem? Can't we just require them to take a ref > on the page (IIRC Jack said GRU could be changed to more like a TLB > model).
Maintaining a long-term reference on a page is a problem. The GRU does not currently maintain tables to track the pages for which dropins have been done. The GRU has a large internal TLB and is designed to reference up to 8PB of memory. The size of the tables to track this many referenced pages would be a problem (at best). ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
